1. Field of the Invention
The present invention relates to a semiconductor light-emitting device, and more particularly, it relates to a semiconductor light-emitting device including an electrode layer exhibiting a high plasma frequency.
2. Description of the Background Art
In general, it is known as possible to excite surface plasmon (electronic oscillation) in a semiconductor light-emitting device by forming a metal layer exhibiting a high plasma frequency in a periodic structure, as disclosed in “Coupling of InGaN quantum-well photoluminescence to silver surface plasmons”, Phys. Rev. B60, 11564–11567, 15 October 1999, for example. It is possible to improve emission efficiency and light extraction efficiency by effectively utilizing the surface plasmon (electronic oscillation).
Assuming that real parts of the dielectric constants εA and εB of a metal A and a dielectric B (including air or vacuum) have inverse signs, a light wave (electromagnetic wave) having intensity exponentially attenuating in two perpendicular directions is present on the interface between the metal A and the dielectric B in the following case:εA+εB<0This electromagnetic wave is referred to as surface plasmon. The dielectric constant εA of the metal A is generally expressed as follows:εA=ε0(1−ωP2/ω2)where ε0 represents the dielectric constant of vacuum, ω represents the frequency of light, and ωP represents a value referred to as a plasma frequency. If the dielectric B is vacuum, surface plasmon is present with an angular frequency smaller than the following value:ωS=ωP/20.5The value ωS is generally in the visual or ultraviolet wave range.
In order to attain the surface plasmon effect with respect to short-wavelength light in a semiconductor light-emitting device, a metal such as silver or aluminum exhibiting a high plasma frequency must be employed.
When an electrode of silver or aluminum for attaining the surface plasmon effect is formed on the surface of a p-type semiconductor layer in a short-wavelength semiconductor light-emitting device such as an AlGaInN-based light-emitting device, however, it is disadvantageously difficult to attain excellent ohmic contact.